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Title: Rheometry for gel point detection
Author: Hawkins, K. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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Various types of rheometry for gelling systems, in particular for detection of a Gel Point, have been investigated. Such rheometry will require rapid measurements and invoke small strains in order to Theologically characterise strain-sensitive materials, such as gelling systems. The Gel Point is of wide scientific and engineering interest. Prior to the Gel Point the material may be readily processed whilst in a Post gel state the material hinders flow processes but provides a measure of long term mechanical stability. It is often vital that all flow processes are carried out prior the Gel Point. The Gel Point represents the case where the connectivity spans the entire sample. In terms of the Winter-Chambon gel Equation, which represents a rheological 'equation of state' of the critical gel, and is characterised by a power-law dependence of the stress relaxation modulus. This power law yields a stress relaxation exponent, a, which has been shown to be related to a fractal dimension, df The fractal dimension is extremely important in terms of the structural characteristics of the critical gel. The Gel Point, as represented by the Winter-Chambon Gel Equation infers a frequency independent loss tangent. This characteristic frequency independent loss tangent provides us with a convenient method of detecting the Gel Point, which may be exploited by various rheometrical means. This thesis examines various rheometrical techniques, including low frequency dynamic testing and high frequency shear wave propagation, and their applicability to detect the Gel Point. In particular, much of the work herein has focussed on determining the linear viscoelastic ranges of transient systems by utilising a Fourier analysis procedure, whereby the response of an imposed strain is sampled. A criterion has been developed which unambiguously determines the onset of a nonlinear rheological response. Linear viscoelastic measurements using various rheometers have been conducted on a gelling system, to determine its Gel Point and associated gel properties. The process industry demands a highly robust and sensitive rheometer suitable for online detection of the Gel Point. A new type of sensor which utilises the Giant Magneto Impedance effect is extremely robust and sensitive. This sensor is the Amorphous Wire Transducer and initial tests have been conducted with a view to employing such sensors on high frequency rheometers, such as the Pulse Resonance Rheometer and Virtual Gap Rheometer.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available